Rotary mechanism control with power supply

ABSTRACT

The invention relates to a hydraulic controller, in particular for the control of the rotating mechanism of an excavator. In a hydraulic drive circuit a drive hydraulic pump ( 2 ) and a drive hydraulic motor are provided, which are connected via working lines ( 3, 4 ). The hydraulic controller includes an adjustment arrangement ( 9 ) for adjusting a setting piston ( 12 ) arranged between two setting pressure chambers ( 10, 11 ) and acting upon the displacement volume of the drive hydraulic pump ( 2 ). Further, a pre-control arrangement ( 8 ) is provided which acts upon one of the setting pressure chambers ( 10, 11 ) with a setting pressure, in dependence upon the pressure difference between two control lines ( 6, 7 ). In accordance with the development according to the invention, the precontrol arrangement ( 8 ) is connected with a feed line ( 30 ) via a pressure regulation valve ( 56 ), whereby the precontrol arrangement ( 8 ), in a control position ( 42, 43 ), connects one of the two setting pressure chambers ( 10; 11 ) with the feed line ( 19 ) via the pressure regulation valve ( 56 ) and connects the respective other setting pressure chamber ( 11; 10 ) with a pressure fluid tank ( 17 ). In a neutral position ( 41 ), both setting pressure chambers ( 10, 11 ) are connected with the feed line ( 30 ) via the pressure regulation valve ( 56 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hydraulic controller, in particular for thecontrol of the rotating mechanism of an excavator.

2. Discussion of the Prior Art

A hydraulic controller in accordance with the State-of-the-technology isdisclosed e.g. in DE 44 05 472 A1. The hydraulic circuit diagram of thisknown hydraulic controller is, for better understanding of theinvention, reproduced in FIG. 2 of the drawings and will be brieflydescribed below with reference to FIG. 2.

The known rotating mechanism controller 1, illustrated in FIG. 2,includes a drive hydraulic pump 2 which is connected via working lines3, 4 with a drive hydraulic motor (not shown) for the drive of therotating mechanism (likewise not shown) of an excavator. The hydrauliccontroller includes a hand controller 5 which is in connection with apre-control arrangement 8 via control lines 6 and 7. By means of thepre-control arrangement 8, the necessary setting pressure is deliveredto an adjustment arrangement 9, which setting pressure is obtaineddirectly from the control pressure prevailing in the control lines 6, 7.The adjustment arrangement includes a setting piston 12, arrangedbetween two setting pressure chambers 10 and 11, which setting pistonacts upon the displacement volume of the working hydraulic pump 2.

Upon return of the hand controller 5 into its neutral position, thepre-control arrangement 8 likewise takes up its neutral position, sothat the adjustment arrangement 9 is no longer supplied with hydraulicenergy, i.e. with setting pressure. The working hydraulic pump 2 isslowly swung back to zero displacement volume via the return springs 13and 14. Thereby, from an after-suction arrangement 74, which consists ofthe check valves 15 and the after-suction filter 16, pressure fluid isdrawn into that setting pressure chamber 10 or 11 the volume of whichincreases in the return procedure.

This known rotating mechanism controller has, however, several gravedisadvantages. Through the after-suction of pressure fluid out of thepressure fluid tank 17, particles of dirt can penetrate into thehydraulic controller. This problem can be only partially removed even bymeans of the after-suction filter 16. Since, during the after-suctionprocedure, only slight pressure differences prevail, the filter must berelatively large, which conflicts with the goal of a lesserconstructional size of the hydraulic controller. Beyond this, theafter-suction filter 16 must be regularly cleaned and serviced.

Insofar as particles of dirt penetrate into the pre-control arrangement8 and lock this in one of its control positions, operational safety isput significantly at risk. The valve of the pre-control arrangement 8 isthereby not returned into its neutral position, but remains in one ofits control positions. If, now, the respective other direction ofrotation of the rotating mechanism is set by means of the handcontroller 5, i.e. the respective other control line 6 or 7 is actedupon with control pressure, this does not lead to the intended reversalof the swing-out direction and thus the delivery direction of theworking hydraulic pump 2. Rather, the working hydraulic pump 2 continuesto deliver in its previously set delivery direction, so that thedirection of rotation of the rotating mechanism is, contrary to theintentions of the user, not reversed, but the rotating mechanism isaccelerated in the opposite direction. In practice, this can represent asignificant source of danger.

A further disadvantage arises with the known rotating mechanismcontroller in that in control of the driving hydraulic pump it is notdetected whether pressure fluid in sufficient quantity is available inthe working lines 3 and 4. In this respect, problems can arise inparticular in that the feed filter 18 of the feed arrangement 19 isblocked and the feed pump 20 cannot feed pressure fluid in sufficientquantity into the working circuit 3, 4. Thus, there is a danger ofdamage to the drive hydraulic pump 2 and to the drive hydraulic motor(not shown).

SUMMARY OF THE INVENTION

It is thus the object of the present invention to so further develop theknown hydraulic controller that operational problems e.g. due to thepenetration of dirt particles or the blocking of filters are avoided.

The invention is based upon the insight that by obtaining the settingpressure for the adjustment arrangement from the feed pressure madeavailable by the feed arrangement, two goals are simultaneouslyattained. On the one hand it is ensured that after return of the handcontroller and thus also of the pre-control arrangement into theirrespective neutral positions, filtered pressure fluid, for balancing thevolume differences during the return procedure flows into the settingpressure chambers of the adjustment arrangement. An after-suctionarrangement can be omitted. On the other hand, it is ensured that incase of a failure of the feed arrangement, e.g. through blockage of thefeed filter, no setting pressure is available and thus the workinghydraulic pump swings back into its neutral position. Thus, damage tothe working hydraulic pump and the working hydraulic motor is reliablyavoided in the case of this fault.

The pre-control arrangement can be constituted in per se known manner asa 4/3-way valve. However, it is more advantageous, corresponding toclaim 3, to form the pre-control arrangement in a divided manner, withseparate valve regions each respectively for one control pressurechamber of the adjustment arrangement. By these means, a separatecontrol of the right and left slewing of the rotating mechanism isattained. Insofar as with this arrangement dirt particles might stillpenetrate into the valve of the pre-control arrangement and block thisin one of its control position, it is ensured that upon change of thecontrol direction by means of the hand controller and correspondingreversal of the pressure action on the control lines 6 and 7 nounintended acceleration of the rotating mechanism in the previouslyselected, opposite direction occurs. The pre-control arrangement can inthis case be formed as a 6/3-way valve.

Corresponding to the invention, the pressure regulation valve providedbetween the feed arrangement and the pre-control arrangement, or—in thecase of separate control of left and right slewing—the two pressureregulation valves provided, set the setting pressure to the controlpressure prevailing in the control line or a slightly higher pressure.The pressure difference between the control pressure and the settingpressure can be attained by means of spring action on the pressureregulation valve or the pressure regulation valves.

Corresponding to the invention, a pressure cut-off valve may be providedbetween the control pressure lines and the pressure fluid tank, in orderto limit the pressure in the control lines to a predetermined maximumpressure.

Further, corresponding to the invention, a brake valve may be provided,in order to make possible a slow, delayed breaking of the rotatingmechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in more detail with reference totwo preferred exemplary embodiments and with reference to the drawings.In the drawings:

FIG. 1 shows a first exemplary embodiment of the hydraulic controller inaccordance with the invention,

FIG. 2 shows a hydraulic controller corresponding to the state of theart,

FIG. 3 shows a second exemplary embodiment of the hydraulic controllerin accordance with the invention,

FIG. 4 shows, in schematic representation, a pressure regulation valveemployed with the hydraulic controller in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a first exemplary embodiment of the hydraulic controller 1in accordance with the invention.

The drive of the rotating mechanism is effected via a drive hydraulicmotor (not shown) which is located in a hydraulic working circuit formedby means of the working lines 3 and 4, which circuit is supplied fromthe working hydraulic pump 2. The after-feed of leakage losses into thehydraulic circuit 3, 4 is effected by means of the feed arrangement 19which includes a feed pump 20. The feed pump 20 is in the exemplaryembodiment coupled to the working hydraulic pump 2 and draws pressurefluid out of the pressure fluid tank, via the feed filter 18, and feedsthis pressure fluid into the feed line 30. The feed line 30 is connectedwith the working lines 3 and 4 via check and pressure regulation valves31 and 32, in order to feed the pressure fluid into the respectiveworking line 3 or 4 carrying the lower pressure. By this means it isensured that in the working circuit 3, 4 pressure fluid is available insufficient quantity as working medium. For avoiding an over-pressure inthe feed line 30, there is further provided an over-pressure valve 33which connects the feed line 30 with the pressure fluid tank 17.

The control of the working hydraulic pump 2 is effected in the exemplaryembodiment manually by the operator via the hand controller 5, which isconnected with a control pressure in-feed 35 via a control line filter34. In dependence upon the intended direction of rotation of therotating mechanism, the hand controller 5 delivers a control pressureinto one of the two control lines 6 or 7, the height of which pressureis proportional to the intended torque. The respective other controlline in each case, 7 or 6, is vented via the tank line 36.

The control lines 6 and 7 are led to the pre-control chambers 39 and 40of the pre-control arrangement 8, via throttle points 37 and 38. Thepressure difference between the pre-control chambers 39 and 40 effects adisplacement of the valve body 41 of the pre-control arrangement 8 intoone of the two control positions 42 or 43, depending upon which of thecontrol lines 6 or 7 is acted upon with the control pressure.

In the control positions 42 or 43 of the pre-control arrangement 8, oneof the setting pressure chambers 10 or 11 is acted upon with a settingpressure, whilst the respective other setting pressure chamber 11 or 10is connected with the pressure fluid tank 17 via the tank line 44 andthe brake valve 45 to be described in more detail.

The consequential displacement of the setting piston 12 brings about aswinging out of the working hydraulic pump 2 in the desired direction ofdelivery, so that the drive hydraulic motor (not shown), and therotating mechanism driven thereby, is accelerated in the intendeddirection of rotation. For the mechanical return arrangement 46, areturn force proportional to the displacement of the setting piston 12out of its neutral position is exercised on the pre-control arrangement8, where this is known in principle from DE-OS 41 25 706. Further, thereare provided compensation lines 47 and 48 connected with the workinglines 3 and 4, so that the pressure difference arising between theworking lines 3 and 4 acts in a force compensating manner on thedisplacement of the valve body 41 of the pre-control arrangement 8.

A pressure cut-off valve 50 is arranged between a change-over valve 49,connected with the control pressure lines 6 and 7, and the pressurefluid tank 17. The pressure cut-off valve 50 effects a pressurelimitation of the control pressure prevailing in the respectivepressure-carrying control pressure line 6 or 7, whereby the maximumpressure can be predetermined via an electromagnetic setter 51.

Further, a brake valve 45 is provided which makes possible a controlledand sensitive braking. The brake valve 45 is arranged between the tankline 44, connected with the precontrol arrangement 8, and the pressurefluid tank 17. The brake valve 45 is on the one hand acted upon by thecontrol pressure prevailing in the control lines 6 and 7, via thecontrol pressure connection line 52 and the change-over valve 49, and isacted upon on the other hand by the working pressure prevailing in theworking line 3 or 4 on the high pressure side, via the working pressureconnection line 53 and the change-over valve 54. When the handcontroller 5 is returned into its neutral position, and thus the controlpressure in the control pressure lines 6 and 7 falls, but a workingpressure is still present in the high pressure side working line 3 or 4,the brake valve 45 is displaced into its throttled valve position 55, sothat the corresponding setting pressure chamber 10 or 11 is vented tothe pressure fluid tank 17 only with delay and thus the brakingprocedure is delayed.

Corresponding to the further development in accordance with theinvention, the setting pressure is not obtained directly from thesetting pressure lines 6 and 7, but indirectly via a pressure limitingvalve 56 from the feed pressure prevailing in the feed line 30. For thispurpose, the pre-control arrangement 8 is connected with the feed line30 via a setting pressure line 57, the pressure regulation valve 56 andthe throttle point 58. The pressure regulation valve 56 therebyregulates the setting pressure prevailing in the setting pressure lineto a pressure level which is provided from the force equilibrium betweenon the one hand the control pressure of the pressure-carrying controlpressure line 6 or 7, delivered via the control pressure connection line52 and the change-over valve 49, and the spring action by means of thepressure spring 59 and, on the other hand, the setting pressuredelivered via the by-pass line 60. Thereby, a setting pressure arises inthe setting pressure line 57 which, due to the spring action by means ofthe pressure spring 59, is slightly higher than the control pressureprevailing in the pressure-carrying control pressure line 6 or 7. Thepressure difference between the setting pressure and the controlpressure is preferably 1 to 2 bar and can be set via the adjustablepressure spring 59.

When the hand controller 5 is returned into its neutral position, inwhich there thus prevails no control pressure in the control pressurelines 6 and 7 and thus the valve body 41 of the pre-control arrangement8 is returned into its neutral position 61, the setting pressurechambers 10 and 11 of the adjustment arrangement 9 are connected via thepressure regulation valve 56 with the feed line 30. By means of thepressure spring 59 it is ensured that the pressure fluid can flow back,via the setting pressure line 57 and the pre-control arrangement 8, intothe setting pressure chambers 10 and 11, when the setting piston 12 isreturned into its neutral middle position due to the return springs 13and 14. The pressure fluid necessary for the volume equalization in thesetting pressure chambers 10 and 11 is thus, corresponding to thedevelopment in accordance with the invention, not drawn in via anafter-suction arrangement from the pressure fluid tank 17, but isdelivered via the pressure regulation valve 56 out of the feed line 30.Since the pressure fluid in the feed line 30 is filtered by the feedfilter 18 and is largely free from dirt particles, a contamination ofthe pre-control arrangement 8 and the setting pressure chambers 10 and11 during the return procedure is reliably avoided, particularly in thatthe connection to the tank line 44 is broken in the neutral position 61of the pre-control arrangement 8. By means of the pressure spring 59 itis ensured that also after fall of the setting pressure in the settingpressure lines 6 and 7 to zero, a slight pressure of preferably 1 to 2bar is maintained in the setting pressure line 57, which is sufficientfor the after-flow of the pressure fluid into the setting pressurechambers 10 and 11 during the return procedure.

By means of the development in accordance with the invention it isensured that always filtered oil from the feed line 30 is delivered tothe pre-control arrangement 8 and the adjustment arrangement 9. Thereby,a contamination of these arrangements is reliably avoided. Further, anafter-suction arrangement having a relatively large after-suction filtercan be omitted, so that the hydraulic controller in accordance with theinvention can be configured constructionally more compactly. Further,the adjustment arrangement is continuously supplied with oil.

A further substantial advantage is provided by the fact that the settingpressure is derived from the feed pressure. As a consequence of adisruption of operation in the feed arrangement 19, in particular due toblockage of the feed valve 18, it can occur that the leakage losses inthe working circuit 3, 4 can no longer be compensated by means of thefeed arrangement 19. In order to avoid damage to the working hydraulicpump and the working hydraulic motor, it is absolutely necessary in thisfault condition to swing back at least the working hydraulic pump 2 tozero displacement volume. This is automatically achieved by means of thedevelopment in accordance with the invention, since with a fall of thefeed pressure in the feed line 30 there is linked simultaneously a fallof the setting pressure in the setting pressure line 57, so that theworking hydraulic pump can no longer be swung out by the adjustmentarrangement 9.

FIG. 3 shows a further exemplary embodiment of the invention with anadditional development. The elements already described with reference toFIG. 1 are provided with corresponding reference signs, so that withregard thereto a repeated description is not necessary.

In contrast to the exemplary embodiment according to FIG. 1, with theexemplary embodiment according to FIG. 3 the control for the right andleft slewing of the rotating mechanism is separately constituted. Forthis purpose, the valve body 41 of the pre-control arrangement 8 hasseparate valve regions 42 a, 61 a, 43 a and 42 b, 61 b and 43 b. A valveregion 42 a, 61 a, 43 a having the control positions 42 a and 43 a andthe neutral position 61 a, serves for control of the setting pressurechamber 11. In contrast, the valve region 42 b, 61 b, 43 b, havingcontrol positions 42 b and 43 b and the neutral position 61 b, servesfor control of the control pressure chamber 10. The two valve regionsare accommodated in a unitary valve body 41. The functioning of this6/3-way valve is largely the same as that of the 4/3-way valve whichfinds employment in the exemplary embodiment according to FIG. 1.

For each valve region of the pre-control arrangement 8 there is provideda separate pressure regulation valve 56 a and 56 b, which are bothconnected with the feed line 30 via the throttle point 58. By means ofthe pressure regulation valve 56 a, the pressure in the setting pressureline 57 a is regulated substantially to the control pressurepredetermined by means of control line 6, whereby the pressure in thecontrol pressure line 57 a is slightly larger than the control pressurein the control line 6 due to the pressure spring 59 a. The same appliesto the pressure regulation valve 56 b, whereby the setting pressure inthe setting pressure line 57 b is regulated substantially to the controlpressure prevailing in the control line 7, but is slightly greater thanthe control pressure prevailing in the control line 7 due to thepressure spring 59 b.

The separation of the control for right and left slewing has theadvantage that in the case of a blockage of the pre-control arrangement8 as a consequence of the penetration of dirt particles, no dangerousfault condition appears. Whilst with the exemplary embodiment accordingto FIG. 1, in the same manner as also with the state of the artreproduced in FIG. 2, upon a blockage of the pre-control arrangement 8in one of its control positions 42 or 43, and a subsequent change of thepressure side in the control lines 7 and 6, a further slewing of therotating mechanism is caused, without the intended change of directionof rotation, this fault condition is avoided with the exemplaryembodiment according to FIG. 3. When, with the exemplary embodimentaccording to FIG. 3, the pre-control arrangement 8 is blocked on one ofits control positions, e.g. in the control position 42 a and 42 b, thismeans that the setting pressure chamber 11 is connected with the feedline 30 via the pressure regulation valve 56 a and the setting pressurechamber 10 is connected with the pressure fluid tank 17 via the tankline 44. If now, as a consequence of an intended change of direction ofrotation of the controlled rotating mechanism, the control line 7,instead of the control line 6, is acted upon with control pressure bymeans of the hand controller 5, this brings about no more swinging-outof the drive hydraulic pump 2, since the connection with the settingpressure line 57 b is cut off due to the blocking of the pre-controlarrangement 8 in the control position 42 b. The setting pressure chamber10 is thereafter, in this fault condition, not acted upon with settingpressure. Differently than with the exemplary embodiment according toFIG. 1, however, the setting pressure chamber 11 is not acted upon inunintended manner with setting pressure, since the setting pressurechamber 11 is connected with the setting pressure line 57 a via thepre-control arrangement 8 blocked in the control position 42 a. Thesetting pressure line 57 a is, however, substantially pressureless sincethe setting pressure prevailing in the setting pressure line 57 a ispredetermined via the pressure regulation valve 56 a by the controlpressure prevailing in the control line 6. Since, after reversal of theintended direction of rotation, the control line 6 is pressureless, nodefective swinging-out of the drive hydraulic pump 2 in the non-intendedoriginal direction of delivery occurs. Thus, an acceleration of therotating mechanism in the non-intended direction of rotation iseffectively prevented.

With regard to the replacement, in accordance with the invention, of theafter-suction arrangement by an oil feed from the feed line 30,controlled via the pressure regulation valves 56 a and 56 b, referencecan be made to the advantages indicated above.

FIG. 4 shows an exemplary embodiment of a pressure regulation valve 56,56 a and 56 b employed within the scope of the present invention.

The setting pressure line 56 is connected via a first control edge 70with the pressure fluid tank 17 and via a second control edge 71 withthe feed line 30. A first pressure chamber 72 is connected via thecontrol pressure connection line 52 with one of the control lines 6 or7, whilst a second pressure chamber 73 is connected with the settingpressure line 57 via a by-pass line 60. Further, there is provided inthe first pressure chamber 72 a preferably adjustable pressure spring59. Through the balance of forces which arises, the pressure in thesetting pressure line 57 is set to a slightly higher pressure than thecontrol pressure prevailing in the control pressure connection line 52.The difference between the setting pressure prevailing in the settingpressure line 57 and the control pressure predetermined via the controlpressure connection line 52 corresponds to the additional force causedby means of the pressure spring 59. The pressure difference between thesetting pressure and the control pressure is preferably 1 to 2 bar.

The invention is not restricted to the illustrated exemplaryembodiments. In particular, the concrete configurations of thepre-control arrangement and of the adjustment arrangement can, withinthe scope of the present invention, be differently provided. As apressure regulation valve 56, 56 a and 56 b there can be employed knownpressure regulation valves of any construction.

What is claimed is:
 1. Hydraulic controller for the control of arotating mechanism of an excavator comprising: a hydraulic drive circuit(2, 3, 4) with a drive hydraulic pump (2) and a drive hydraulic motor,and two working lines (3, 4) connecting the drive hydraulic pump (2) andthe drive hydraulic motor, a feed arrangement (19) for feeding pressurefluid into the drive circuit (2, 3, 4), an adjustment arrangement (9)for adjusting a setting piston (12) arranged between two settingpressure chambers (10, 11) and acting upon the displacement volume ofthe drive hydraulic pump (2), a pre-control arrangement (8) which actsupon the setting pressure chambers (10, 11) with a setting pressure independence upon the pressure difference between two control lines (6,7), and said pre-control arrangement (8) including a pressure regulationvalve (56) which is connected with the feed arrangement (129), thepre-control arrangement (8) when in a control position (542, 43),connecting one of the two setting pressure chambers (10; 11) with thefeed arrangement (19) via the pressure regulation valve (56) andconnecting the respective other setting pressure chamber (11; 10) with apressure fluid tank (17) and, when in a neutral position (41),connecting both setting pressure chambers (10, 11) with the feedarrangement (19) via the pressure regulation valve (560, and wherein thepressure regulation valve (56) sets the setting pressure to a pressurewhich is at least slightly higher than the control pressure prevailingin the control line (6, 7) having a higher pressure.
 2. Hydrauliccontroller according to claim 1, wherein the pre-control arrangement (8)includes a 4/3-way valve.
 3. Hydraulic controller according to claim 1,wherein the feed arrangement (19) includes a feed pump (20) which isconnected with the working lines (3, 4) via check valves (31, 32). 4.Hydraulic controller according to claim 1, wherein a pressure cut-offvalve (50) is provided between the control lines (6, 7) and the pressurefluid tank (17), said pressure cut-off valve limiting the pressure inthe control lines (6, 7) to a predetermined maximum pressure. 5.Hydraulic controller according to any one of claims 1 to 4, wherein abrake valve (45) is provided between the pre-control arrangement (8) andthe pressure fluid tank (17), said brake valve throttling the connectionbetween the setting pressure chambers (10, 11) and the pressure fluidtank (17) in dependence upon the pressure difference between the controlpressure line (6, 7) having a higher pressure and the working line (3,4) having a higher pressure.
 6. Hydraulic controller for the control ofa rotating mechanism of an excavator, comprising: a hydraulic drivecircuit (2, 3, 4) with a drive hydraulic pump (2) and a drive hydraulicmotor, and two working lines (3, 4) connecting the drive hydraulic pump(2) and the drive hydraulic motor, a feed arrangement (19) for feedingpressure fluid into the drive circuit (2, 3, 4), an adjustmentarrangement (9) for adjusting a setting piston (12) arranged between twosetting pressure chambers (10, 11) and acting upon the displacementvolume of the drive hydraulic pump (2), a pre-control arrangement (8)which acts upon the setting pressure chambers (10, 11) with a settingpressure in dependence upon the pressure difference between two controllines (6, 7), and the pre-control arrangement (8) including two pressureregulation valves (56 a, 56 b), which are connected with the feedarrangement (19), the pre-control arrangement (8) has two separate valveregions (42 a, 61 a, 43 a; 42 b, 61 b, 43 b) each for connecting one ofthe two setting pressure chambers (10, 11) with one of the two pressureregulation valves (56 a, 56 b), whereby the pre-control arrangement (8),in a control position (42, 43), connects one of the two setting pressurechambers (10; 11) with the feed arrangement (19) and connects therespective other setting pressure chambers (11; 10) with a pressurefluid tank (17) and, in a neutral position (41), connects both settingpressure chambers (10, 11) with the feed arrangement(19).
 7. Hydrauliccontroller according to claim 6, wherein the pre-control arrangement (8)includes a 6/3-way valve.
 8. Hydraulic controller according to claim 6,wherein the feed arrangement (19) has a feed pump (20) which isconnected with the working lines (3, 4) via check valves (31, 32). 9.Hydraulic controller according to claim 6, wherein the pressureregulation valves (56 a, 56 b) set the setting pressure based on thecontrol pressure prevailing in the control line (6, 7) having a higherpressure.
 10. Hydraulic controller according to claim 6, wherein thepressure regulation valves (56 a, 56 b) set the setting pressure to apressure which is slightly higher than the control pressure prevailingin the control line (6, 7) having a higher pressure.
 11. Hydrauliccontroller according to claim 6, wherein a pressure cut-off valve (50)is provided between the control lines (6, 7) and the pressure fluid tank(17), which pressure cut-off valve limits the pressure in the controllines (6, 7) to a predetermined maximum pressure.
 12. Hydrauliccontroller according to claims 6 to 11, wherein a brake valve (45) isprovided between the pre-control arrangement (8) and the pressure fluidtank (17), which brake vale throttles the connection between the settingpressure chambers (10, 110 and the pressure fluid tank (17) independence upon the pressure difference between the control pressureline (6, 7) having a higher pressure and the working line (3, 4) havinga higher pressure.